Temperature compensation of the sprung balance oscillator has traditionally been obtained through the use of a bimetallic balance wheel and a steel balance spring. The discovery of Elinvar by Ch. Ed Guillaume made it possible to simplify the oscillator by associating a monometallic balance with a compensated balance spring made of Elinvar. Different variants of the alloy then appeared under various different trade names such as “Nivarox”, “Isoval”, “Durinval”, “Ni-span C”, etc.
All these alloys have the drawback of reacting strongly to magnetic fields since they are ferromagnetic in nature.
It is an object of the present invention to propose a compensating alloy that is insensitive to magnetic fields.
Horological research has always sought to develop new alloys, having particular specifications, as regards temperature resistance, or the non-magnetic or antiferromagnetic nature of the alloys.
For example, CH Patent 286912 in the name of ELGIN discloses a spring made of a cobalt-chromium-nickel alloy with 20 to 60% cobalt, 15 to 30% chromium, less than 18% iron, from 0.01 to 0.09% beryllium, from 0.05 to 0.30% carbon, with a nickel-iron total comprised between 20 and 40%, and a nickel content greater than that of iron. U.S. Pat. No. 2,419,825 in the name of DINERSTEIN also discloses a spring alloy with a high elastic limit, with 30% nickel, 9% chromium, 1.5% manganese, 1% silicon, 0.3% tungsten, 0.06% carbon in the form of chromium carbide, 0.5% beryllium, traces of calcium, and the remainder iron, with a very particular production cycle. CH Patent 196408 in the name of INSTITUT STRAUMANN discloses a temperature compensating spring made of a heat-treatable alloy of nickel-iron-molybdenum-beryllium, in different compositions always having more than 35% nickel, more than 7% molybdenum, quite a variable percentage of beryllium within the range of 0.1% to 1%, and always less than 3% chromium.
Alloys of the iron-manganese-nickel-chromium type are acceptable for theoretically having good antiferromagnetic qualities, and, more specifically, iron-manganese-nickel-chromium-beryllium alloys. However, it is very difficult to determine compositions and methods of production that can ensure, in a reproducible manner, good temperature compensation characteristics, with as flat a range as possible, within the usual watchmaking temperatures, typically from 8° C. to 38° C., to avoid the use of the bimetallic materials normally used to compensate for thermal drifts.
Indeed, even if a particular composition should be capable of particular thermal properties, the production of such alloys proves extremely difficult, and very slight differences in certain parameters lead to a wide range of results. Routine testing cannot possibly lead a metallurgist to the desired performance.
Cold forming the components only adds to the complexity of the task, because of the large number of operating parameters relating, on the one hand, to the production of the alloy, and on the other hand, to the shaping thereof.